Polyketone compositions, linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon, such as ethylene, can be prepared using a catalyst formed from using a palladium compound, an anion of a non-hydrohalogenic acid, and a quaternary phosphonium compound bidentate ligand of the general formula EQU R.sup.1 R.sup.2 --P--R--P--R.sup.3 R.sup.4
where R.sup.1 -R.sup.4 are organic radicals, such as aryl and R is a divalent bridging group, such as alkylene. Recent examples of disclosures of such processes can be found in U.S. Pat. Nos. 4,804,739 and 4,818,810 which are each incorporated herein by reference.